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Thursday, 22 October 2015

A year after the 'Spinosaurus reboot' as a small-legged, early whale-mimicking aquatic quadruped, experts remain divided over fundamental aspects of Spinosaurus palaeobiology. This depiction shows Spinosaurus aegyptiacus as generally imagined prior to 2014.

The long, tragic and occasionally controversial research history of the giant, enigmatic theropod Spinosaurus aegyptiacus will be familiar to many readers of this blog*. First named and described in the early 20th century by Ernst Stromer from remains found in Late Cretaceous strata of Egypt, our principle Spinosaurus material fell victim to Allied bombing raids in World War II and was completely destroyed. Stromer's detailed illustrations and descriptions are all that remains of this material, and these have formed a variably interpreted foundation of all subsequent Spinosaurus research. For much of the 20th century the life appearance of Spinosaurus remained mysterious. Depicted as a nondescript sailed giant theropod early on, discovery of well represented spinosaurids like Baryonyx and Suchomimus, as well as fragments of new Spinosaurus material, permitted more confident interpretations of Spinosaurus size and form as we approached the new millennium. By the 2010s, Spinosaurus was recognised as a gigantic, derived and perhaps semi-aquatic spinosaurid, adapted for feeding on large aquatic prey (above). Much of this interpretation relied on new Spinosaurus remains from multiple locations in northern Africa, including the famous Moroccan Kem Kem Beds, an expanse of Late Cretaceous rocks roughly contemporaneous with those Egyptian deposits yielding the original, destroyed Spinosaurus remains.

Famously, last year saw Spinosaurus reinvented again, this time as a quadrupedal, knuckle-walking, long-bodied, tiny-legged dinosaurian take on a crocodile or early whale (below). The authors of this widely publicised study, Nizar Ibrahim and colleagues (2014), synthesised existing and new data on African spinosaurids to create this reconstruction, synonymising several taxa into S. aegyptiacus and presenting new Spinosaurus remains obtained from the Kem Kem beds. The most significant of these was a set of associated vertebrae, pelvic and hindlimb remains which were proposed as a neotype specimen for Spinosaurus (a specimen to hold the Spinosaurus name now that the original material is lost to science). That this neotype represents Spinosaurus was bolstered by it bearing similar hindlimb and vertebral proportions to 'Spinosaurus B', a collection of Egyptian spinosaurid specimens described by Stromer, considered referable to Sp. aegyptiacus by Ibrahim and colleagues. Spinosaurus B is also now lost, also being destroyed in WWII. The Ibrahim et al. study provided a lot of new data on Spinosaurus and has helped cement the concept of it being a semi-aquatic animal, but several aspects of the paper didn't meet the warmest receptionfrom a number of academics. Specific issues were scaling of the skeletal components, how sensible it was to lump so much north African spinosaurid material into one species, and uncertainty about the provenance of the neotype specimen. Some of these concerns were diffusedby the authors, but we await a promised monograph for answers to all the questions raised by their first paper. In the mean time, the 2014 Spinosaurus interpretation remains a debated topic among those interested in dinosaur palaeontology.

The Ibrahim et al. (2014) take on Spinosaurus aegyptiacus. Different colours represent different specimens: red is the neotype; brown is the original Spinosaurus material; yellow is referred, isolated Spinosaurus remains; green bones are borrowed from other spinosaurids, and blue bones are crafted to fit the skeleton based on neighbouring elements. Image borrowed from Smithsonian.com.

One year later...

This week, the Spinosaurus tale has taken another twist with publication of a mammoth (open access) paper penned by a team of European spinosaurid experts, led by Serjoscha Evers. Evers et al. have reappraised the affinities of Moroccan specimens seemingly related to Spinosaurus: Sigilmassasaurus brevicollis and Spinosaurus maroccanus. These animals, known only from vertebrae, were subsumed into Sp. aegyptiacus by Ibrahim et al. (2014) as part of their trans-African Spinosaurus concept, and that decision is a core focus of the Evers et al. paper. Their work contains extensive commentary on the detailed anatomy of Moroccan spinosaur material and what it might mean for recent interpretations of Spinosaurus form and lifestyle. Given the wide interest in Spinosaurus and the 2014 reconstruction, I thought it might be of interest to summarise some of what they outline here.

Firstly, taxonomic revisions proposed by Evers et al. present a very different picture of what fossils we can identify as belonging to Spinosaurus. Their work on Si. brevicollis and Sp. maroccanus suggests these species are probably one and the same (the latter being sunk into the former), and that Sigilmassasaurus should be considered distinct from Sp. aegyptiacus. They go on to suggest that other Kem Kem vertebrae hint at a second spinosaurid species in the Kem Kem fauna, and outline several reasons why the Ibrahim et al. 'neotype' specimen cannot be referred to Spinosaurus. For one, the neotype is anatomically quite different from Stromer's Egyptian 'Spinosaurus B' specimen. Ibrahim et al. considered Spinosaurus B as representing Sp. aegyptiacus, but Evers and colleagues argue that Spinosaurus B is anatomically more similar to Sigilmassasaurus than Spinosaurus. Spinosaurus B therefore might have no use for linking any specimens specifically to Sp. aegyptiacus, including that all-important neotype.

In addition to these morphological objections, Evers et al, also raise palaeobiogeographic issues with the 'neotype' referral. Evidence for Egyptian dinosaur species being present in Morocco is scant at best, most data indicating little mixing of eastern and western African dinosaur species during the Late Cretaceous. It would be unusual, then, to find the Egyptian species Sp. aegyptiacus in Morocco. Palaeobiogeography is not a deal clincher for taxonomy of course - careful examination of the neotype and genuine Spinosaurus remains will be the deciding factor here - but it is another stick in the mud for the neotype proposal. Although the exact identity of the 'neotype' specimen is left in the air by Evers et al. - ongoing descriptive work on the specimen needs to be completed to truly assess this - they reject the proposal of the Kem Kem specimen as a Sp. aegyptiacus neotype, and leave Spinosaurus characterised by features in Stromer's illustrations. This is obviously quite a shake up of the suggestions made last year: Spinosaurus 2014 might be a mix of at least two named species, incorporate material of under-appreciated taxonomic importance, and substantial, newly published material might have little, if anything, to do with Spinosaurus.

Moving on, Evers et al. also raise concerns about interpretations of Spinosaurus in context of Kem Kem fossil collecting practises. Museum exhibitions and PR exercises suggest that the Kem Kem yields complete skeletons of dinosaurs and other fossil vertebrates, but the reality is quite the opposite. Kem Kem vertebrates are typically preserved as isolated, often broken bones in multitaxic bone beds (that is, bone beds comprising many species). Associated skeletons of single individuals do occur, but they're relatively rare and rely on precise collecting documentation to prove their authenticity. Unfortunately, historic and recent records of Spinosaurus occurrences and excavation are often poor. We might chalk a lack of historic documentation to the practises and technological limitations of bygone times, but recent issues are caused primarily by the commercial value of Kem Kem fossils. The greater majority of Kem Kem fossils, including dinosaurs, are collected without extensive documentation and then sold by private dealers. Even if localities are recorded, ambiguity often surrounds association of fossil material prior to excavation. Several alleged associated Spinosaurus specimens are meant to have come from single localities, but being from the same place is really only half the battle if they stemmed from multitaxic assemblages. Concordant size of bones might suggest genuine association, but this is not always certain either: Evers et al. report practises where collectors sort loose material from disparate locations into type and size categories before sale - nefarious individuals making fossil skeletons more substantial with unassociated elements is a real problem the world over. It's sad but true that the monetary value associated with substantial vertebrate fossils makes ascertaining their authenticity crucial for subsequent credible interpretation.

Unfortunately, Evers et al. report these factors as affecting virtually all associated Spinosaurus material, including the 'neotype' and the other specimen key to the 2014 reconstruction, Spinosaurus B. In the case of the latter, all we have to go on to establish association are Stromer's notes, which are not quite as detailed as we might like. For the neotype, we know some of the specimen was directly collected in the field, and that other bits were purchased from dealers by two academic institutions over a two year period - exact documentation of this remains to be presented (hopefully it will in the 'neotype' monograph). Without strict certainty over how many individuals these specimens might represent, Evers et al. suggest some of the odd proportions in recent Spinosaurus reconstructions may reflect the marrying of mismatched bones to one another. That's not a certainty, of course, but it's also something which shouldn't be casually ignored.

Collectively, Evers et al. use these points to provide an alternative take on Spinosaurus to that presented in 2014. Ibrahim et al. argued that their new material helped simplify and integrate different interpretations of African spinosaurid material, but Evers et al. argue the opposite: they emphasise how poorly known Spinosaurus and kin are, and how interpreting fossils of north African spinosaurids is getting increasingly complex. Spinosaurus fossils remain very fragmentary to the point where most cannot be directly compared, they seem to hint at, but don't really crystalise, an apparent high species diversity, and are often of uncertain association or exact origin. At face value, that doesn't leave us with a lot to be confident about, although we'll have to see how this more despondent view goes down with other spinosaurid researchers. More complete and well documented discoveries will soon help smooth out bumps in our knowledge, but it seems likely that a lot of work and discussion remains to sort out what is really going on with north African, Late Cretaceous spinosaurids.

What does this mean for 'the Spinosaurus reboot'?

That's not quite the end of our discussion, however. It might be assumed that the points outlined above sound the death knell for the strangely proportioned 2014 Spinosaurus reconstruction, and that we should go back to our traditional interpretation of this animal. That might not be quite right, for two reasons. Firstly, given how distinctive many 'Spinosaurus' remains now seem to be, it's actually questionable what specimens should be considered Sp. aegyptiacus at all, other than the first specimen described by Stromer. A lot of referred isolated Spinosaurus specimens have been incorporated into our 'traditional' reconstructions in recent years, and we might need to think hard about their role in our interpretations of this animal. What we've become typically used to thinking of as Spinosaurus may not entirely be Spinosaurus!

Secondly, while some aspects of the 2014 interpretation of Spinosaurus have clearly been challenged by the Evers et al. paper, not all proportional aspects of the recent Spinosaurus reinvention are obviously erroneous. Last year, Ibrahim et al. noted that both Spinosaurus B and the 'neotype' have reduced hindlimbs with respect to their associated vertebrae, and used this fact as support for the diminutive legs in their reconstruction. Although arguing that there is no longer evidence for short hindlimbs in Spinosaurus itself, Evers et al. don't completely dismiss the notion of some African spinosaurids being short legged. The hindlimb proportions of those specimens is very similar despite the vagaries surrounding fossilisation and exhumation of ancient animal remains, maybe more similar than you'd expect from chance alone. If it is coincidence, it's certainly a startling one.

Stromer's 'Spinosaurus B' material: proportionally similar to the 'neotype' specimen, but does that tell us anything about spinosaurid proportions? Another image borrowed from Theropoda.

However, Evers et al. also attach some important caveats to this point. Stromer's notes clearly state that he did not consider the 'Spinosaurus B' material to represent one individual, and his testimony is the closest thing we have to a report on the excavation of the material. He specifically comments on the hindlimb being too small and slender to match the vertebrae, and thus interpreted them as representing a second individual. Other workers have agreed that this material must represent multiple animals or even several types of dinosaur (discussions about the possibly chimeric nature of Stromer's spinosaur specimens are not new - e.g. Rauhut 2003; Novas et al. 2005). Interpretation of the Spinosaurus B material as representing one animal is thus against some current thought and, of course, Stromer's original declaration. While the 'neotype' specimen might make a case for Stromer being mistaken, we really need to know more about the collection history to ascertain that. We're left with an intriguing set of measurements hinting at the reduced hindlimbs proposed by Ibrahim et al., but little in the way of objective information to explain their significance. The discovery of new specimens is needed to establish whether some spinosaurids were really short-legged, or if confusion of specimen inventories just made it look that way. In short, and no-doubt to the disdain of people who lose sleep about 'what science has done' to one of their favourite theropods, there's still something to play for with these short-legged spinosaurids.

So that's the latest chapter of research in Spinosaurus, then: I don't doubt that it's going to cause a lot of discussion in popular and academic circles. My personal take-home is that we seem to know less about Spinosaurus than might have been recently suggested, or at least that some issues need to be ironed out before we can develop a clear picture of what Spinosaurus is, and what sort of lifestyle it led. I don't know that any recent proposals about this animal have been shot down entirely yet, although clear gauntlets have been established for some of the more extreme ideas suggested in the last few years. It's going to be very interesting to see how others interpret these latest developments in the ongoing Spinosaurus saga, and where our understanding of this animal moves to next.

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Saturday, 10 October 2015

A small flock of Pterodactylus antiquus, represented by small juveniles (left) up to big adults (right) scope out foraging options in a Jurassic marsh. The animal on the right is luring prey to the surface through paddling forefeet, a behaviour common to (at least) several modern gull species.

Pterosaur researchers are infamous for their frequent disagreements over flying reptile evolution, lifestyles and even basic anatomical interpretation. I can certainly attest that there is some truth to this: writing about pterosaurs can be frustrating because of continual need for clarification and digressions to ensure all points of view are represented. But if there's one pterosaur we must have reached a consensus over, one species we must all agree about, surely it's the Late Jurassic, Solnhofen species Pterodactylus antiquus. The holotype of Pterodactylus - below - has been known to us longer than any other pterosaur fossil, this being the specimen which kick-started flying reptile studies in 1780. Since then, it's almost a rite of passage for researchers to see this specimen along with some of the other several dozen Pterodactylus fossils in museums around the world. Pterodactylus has been looked at so much that a general agreement over what it is, and the species it is related to, has more or less been established. Characterised by a long, low skull, simple teeth, a long neck and largish feet, we consider Pterodactylus a relatively early form of pterodactyloid, and most likely a member of the ctenochasmatoid/ archaeopterodactyloid* branch of pterosaur evolution. This puts it in the same lineage as several other familiar species, such as comb-toothed Ctenochasma and twisty-jawed weirdo Cycnorhamphus. We're all basically happy with the idea that our dataset for Pterodactylus is fairly good: 30 specimens (a very conservative estimate) provide numerous complete skeletons and a growth series from small juveniles up to very large adults.

*As with many parts of the pterosaur tree, nomenclature for 'Pterodactylus-line' pterodactyloids is confused by the use of several, conflicting names and definitions. I wasn't kidding about those caveats and digressions.
All that said, some areas of Pterodactylus research remain contentious, and new insights into its anatomy and disparity are still being published more than 200 years after it was discovered. Surprisingly, unlike the way we often gain novel appreciation for familiar taxa - new specimens shedding new light on old problems - much of our recent understanding of Pterodactylus relies on the same, well-worn specimens we've been analysing for centuries. It's actually quite sobering to see specimens which have been interrogated so much still providing talking points, and it makes me wonder what we're missing from those briefly described, rarely analysed specimens comprising so much of our vertebrate fossil dataset. Here, I want to cover some of the new insights provided on Pterodactylus in just the last two years.

The specimen which started it all: the Pterodactylus antiquus holotype. The wingspan of this specimen, preserved in a 'falling forward' posture rather atypical for a Solnhofen pterodactyloid, is about 45 cm.

Anatomy and palaeobiology

Until recently, most of us have been used to seeing Pterodactylus depicted as a crestless species. A privately owned specimen described in 2003 showed that, like many other pterosaurs, this animal bore a set of soft-tissue structures associated with the top and back of the skull (Frey et al. 2003). Specifically, it seems Pterodactylus bore a soft-tissue crest along the posterior region of the head and a pointed, posteriorly-projecting 'occipital lappet' at the back of the skull. The latter, for now at least, seems unique to Pterodactylus. This information is well known to 21st century scholars, but it's less appreciated that these soft tissues were first mentioned almost 100 years ago. Pterodactylus crests were first reported in the 1920s, and the lappets in 1970 (see Bennett 2013). I find it bizarre that we didn't start restoring Pterodactylus with these interesting structures until the 2000s: this seems to be an example of artists and scientists not working together as well as they might.

Unlike other pterosaurs, the soft-tissue crest of Pterodactylus did not seem to anchor on a low, striated bony ridge. The absence of this feature, even when preservation was sublime enough to record soft-tissues and detection methods were of late 20th century quality, was likely a key factor in our general consideration of Pterodactylus as a crestless species. I always found the occurrence of soft-tissue crests without corresponding bony structures an alarming prospect, one implication being that we could be ignorant of soft-tissue crests in a huge number of pterosaur species.

It was somewhat relieving, therefore, to see Chris Bennett reporting a crest-anchoring structure for Pterodactylus in 2013. It's small, and often smooth rather than striated, but Pterodactylus definitely does have a midline ridge for crest anchorage - even the holotype has one when we look close enough. Exactly how extensive these structures were remains unknown thanks to many historic specimens being accidentally damaged during preparation. It's easy to see how this occurred: the crests are low, extremely fragile, and only 0.2 millimetre thick. They'd be hard to detect and avoid damaging even if you were looking for them. Hopefully, preparators working on unprepared specimens can recover intact crests now we know they exist.

The most extensive example of cranial soft tissues known thus far from Pterodactylus. Unfortunately, we're still some way from knowing what shape they took in life, although this specimen indicates that almost half of the skull was covered by the crest and that the lappet was also quite large. Parts of the diagram labelled 'fa' record sediments which fluoresce under UV light - they're likely matrix contaminated by organic seepage from the decaying pterosaur head. They are unlikely to tell us much about the appearance of the animal in life. From Bennett (2013).

Pterodactylus cranial soft tissues are now known to occur in a number of specimens, but it remains unclear how large or what shape the crests were. The lappets seem to be of a consistent size and position, and many curve upwards, but whether they are joined to the rest of the crest (as suggested by Frey et al. 2003) remains to be confirmed (Bennett 2013). At least some aspects of crest and lappet development matches what we see in other pterosaurs, in that we only start picking up evidence of these structures in larger Pterodactylus specimens. There also seems to be a rough correlation between crest proportions and body size. Pterodactylus thus seems to be another pterosaur species where cranial ornament signifies entry into adulthood, suggesting a function of sexual communication (Bennett 2013).

Speaking of adulthood, it was also only recently that we obtained a true sense of how large Pterodactylus may have grown. We typically imagine this animal as small bodied - maybe with a 50 cm wingspan - but a newly described skull and lower jaw (below) makes the first unambiguous case for Pterodactylus reaching at least 1 m across the wings (Bennett 2013). To put this in a modern context, large Pterodactylus would be of comparable size to smaller heron species, and large individuals would have been conspicuous components of the Solnhofen pterosaur fauna. A trend where skull, neck, and limb proportions increase with body size, first intimated by Peter Wellnhofer (1970), seems to hold up in modern interpretations of Pterodactylus specimens. Realising how variable this pterosaur's proportions might have been throughout life has been very informative to recent considerations of Pterodactylus taxonomy.

The mother of all Pterodactylus skulls. A preserved skull length of 142 mm indicates a skull of around 200 mm long in life, and an animal reaching a 1 m wingspan. From Bennett (2013).

One species, two species, or three genera?

This brings us to some of the more contentious recent developments in Pterodactylus studies: just how many species are represented in the Pterodactylus dataset? Many readers will be aware that the name Pterodactylus was once applied to almost any new pterosaur fossil, and around 80 'Pterodactylus' species have existed in the last 200 years (Ford 2013). The taxonomic history of Solnhofen pterodactyloids has been especially mixed up with the name Pterodactylus and, by the end of the 1800s, their taxonomy was in a real tangle. Work in the mid-20th century, particularly by Peter Wellnhofer (1970), streamlined systematic interpretations of Pterodactylus so that, by the 2000s, only two species were considered valid: P. antiquus and P. kochi. A couple of 'hangers on' were still knocking about ('P'. longicollum and 'P'. micronyx), but researchers universally agreed that these animals were not true members of Pterodactylus, and were simply awaiting new generic names (they now have them: Ardeadactylus and Aurorazhdarcho, respectively).

Distinguishing features between kochi and antiquus were subtle, being primarily aspects of tooth shape, tooth number, and proportions of the skull, neck and torso. This is not a new observation, and suggestions that they may represent the same taxon date back to the 1800s. Eventually, studies of Pterodactylus teeth was used to suggest outright synonymy of these two species (Jouve 2004). Many pterosaurs, as with most reptiles, increase their tooth counts with age and size. Jouve realised that the allegedly distinctive tooth count of P. kochi aligned perfectly with tooth numbers predicted for antiquus of comparable body size. At least in this respect, these two species could not be distinguished. More recently, Bennett (2013) bolstered this synonymy with an assessment of kochi proportions, noting that perceived distinctions in skull and body length were reliant on erroneously recorded measurements. Once corrected, kochi proportions were very similar to comparably sized antiquus individuals (there's a lesson there about the importance, and repetition, of basic data recording in this) and, along with Jouve's work, this study eroded the foundations of the kochi/antiquus split considerably. Remaining distinguishing features between these species are rather poorly defined, and certainly not divorceable from effects of growth, preservation and preparation. Finally, after 200 years, it was looking like Pterodactylus taxonomy had finally been tidied up: we have one Pterodactylus species, not two, or 80.

Historically considered to represent Pterodactylus antiquus, recent work argues this specimen (along with some referred material) is a wholly distinct species, and distantly related to P. antiquus. It was recently christened Aerodactylus scolopaciceps. Image from Vidovic and Martill 2014 (this particular version from Steve Vidovic's Mesozoic Monsters blog).

Except... the story doesn't end there. Last year, my University of Portsmouth colleagues Steven Vidovic and David Martill suggested that not only were 'cryptic taxa' present in the Solnhofen Pterodactylus dataset, but that the traditional phylogenetic placement of some Pterodactylus-like animals might be erroneous. Using a variety of methods, Steve and Dave proposed that Pterodactylus contained at least three taxa: antiquus (which they considered the only true member of the genus), kochi (a separate genus in their interpretation, and more closely related to other pterodactyloids than antiquus), and a resurrected Pterodactylus species from the 1800s, scolopaciceps (Vidovic and Martill 2014, see image, above). Steve and Dave created the generic name Aerodactylus for this animal, providing a diagnostic combination of over 10 character states relating to skull shape and proportions, orbit shape, tooth count, neck length, humeral curvature and limb bone robustness. Attempting to establish the relationships of these three 'Pterodactylus' taxa saw Ctenochasmatoidea/Archaeopterodactyloidea dissolve into a paraphyletic spread across the base of Pterodactyloidea. In this topology, antiquus and kochi anchor the base of Pterodactyloidea (without forming an exclusive clade themselves) and scolopaciceps is at the other end of the 'ctenochasmatoid' range, in a sister clade to the rest of Pterodactyloidea.

That's quite a shake up, contradicting virtually all other recently published opinions on the taxonomy and evolution of these animals. But although different, at least some of these ideas are not be untenable. For instance, the idea that Ctenochasmatoidea/Archaeopterodactyloidea might be paraphyletic is suggested by the 'Painten pro-pterodactyloid', an unusual pterosaur specimen revealed two years ago (below, Tischlinger and Frey 2013). This taxon, which shows a Pterodactylus-like skull combined with postcranial features somewhat like those of non-pterodactyloid pterosaurs, suggests aspects of 'ctenochasmatoid' anatomy developed outside of Pterodactyloidea proper. It therefore will not be that surprising if this taxon pulls some 'basal' ctenochasmatoids of traditional lore to the root of Pterodactyloidea once it's included in phylogenetic studies. (Those interested in the influence of the 'Painten pro-pterodactyloid' animal on our understanding of pterosaur evolution might find this previous post of interest).

But do our few dozen Pterodactylus specimens really comprise three, distantly-related species? On this, I'm less certain. We see a lot of variation across Pterodactylus specimens reflecting those aforementioned factors of ontogeny, preservation and preparation - not to mention individual variation. Having played with Pterodactylus data a little myself, and seen a fair share of specimens relevant to these discussions (though I stress not all), I find the arguments for synonymy more compelling than those for splitting Pterodactylus apart. This said, I have no horse in this race and could be persuaded otherwise. What we really need - and a number of folks in pterosaur research have been saying this for a while now - is someone to travel the world exhaustively documenting and illustrating Pterodactylus specimens, ultimately producing a modern synthesis on its anatomy. Such a study would not only be a valuable research aid (the last attempt at this was 50 years ago, which is an age ago in terms of research and publication techniques), but would pack a lot of weight in resolving ongoing, long running disputes in this animal's taxonomy.

Talking about the future of research into Pterodactylus seems like a sensible place to leave off, and I'll summarise in saying that - as with much else in pterosaur research - we're a little while off a complete consensus on Pterodactylus for now. Clearly, although the concept of Pterodactylus is over two centuries old, there's still things learn about it. Who knows what we'll be saying about this most familiar of pterosaurs in years to come?

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References

Bennett, S. C. (2013). New information on body size and cranial display structures of Pterodactylus antiquus, with a revision of the genus. Paläontologische Zeitschrift, 87(2), 269-289.

Jouve, S. (2004). Description of the skull of a Ctenochasma (Pterosauria) from the latest Jurassic of eastern France, with a taxonomic revision of European Tithonian Pterodactyloidea. Journal of Vertebrate Paleontology, 24(3), 542-554.

Tuesday, 6 October 2015

Realising that Recreating an Age of Reptileswas a bit light on sauropod art, I've been beavering away on two additional sauropodoramas* to pad things out a bit. I thought I'd share them here.

*Sauropods are such special animals that they deserve their own nomenclature for most things, including artwork. See, for another example, 'shards of excellence'.

The first is a reworking of a 2013 image of the Wealden (probable) brachiosaur Pelorosaurus conybeari in hammering wind and rain. We know that Wealden climates were subject to storms and intense downpours on occasion (lightning and floods being, of course, key elements in the production of fossil-rich plant debris horizons in certain Wealden deposits) and it stands to reason that any sauropods around when those rains arrived would have got quite wet indeed. I don't say that just casually: the prospects of being a wild animal the size of a house mean that you're actually pretty exposed to just about everything weather can throw at you. When unexpected meteorological fit hits the shan, your options as a giant are pretty limited. Running away is out, because your legs are pillar-like structures adapted for supporting immense weight, not nimble escape. Seeking shelter is not an option either, because you're bigger than everything else around you. You're just too darned huge to do anything but stand there and take it. The life of a sauropod must've been spent baking in the sun, being battered by wind, and drenched in rain. I find that idea quite romantic and evocative as an artist. When painting sauropods, I often wonder how cracked, weathered and worn their skin must've been through a lifetime of battles with changing weather.

Like masts in a storm, three Pelorosaurus conybeari brave typically English weather, c. 135 million years ago. They're doing their best to look tough next to a couple of rainbows.

Second is an image inspired by a recent SVPCA talk by sauropod expert Mike Taylor and his colleagues Matt Wedel, Darren Naish and Brian Engh. Regular readers of the palaeoblogosphere will probably already know where this is going, given that Mike's talk (and the upcoming Wedel et al. paper) has been given some hefty coverage at SV:POW!. Those familiar with sauropods will know that apatosaurines (Apatosaurus, Brontosaurus and a few other taxa) have atypically proportioned, large and robust neck vertebrae, with their cervical ribs being especially elongated and reinforced. These structures possess peculiar buttresses on their underside which, it seems, are not products of muscle or ligament attachment (if they are, they have no modern analogue). Instead, they might relate to an epidermal feature like a boss or horn, as such structures sometimes leave peculiar swellings on underlying bones. Exactly what these anatomies indicate has long been puzzling, and all the more so because all apatosaurines show neck vertebrae with these features. Some (like Brontosaurus) were more extreme than others in development of these features, but even modest apatosaurines were doing crazy, mysterious stuff with their neck anatomy. Question is, what?

Matt, Mike and others have recently been outlining a first principles approach to this conundrum. They note that the reinforced construction of apatosaurine necks, the additional muscle attachment afforded by vertebral expansion, and those strange vertebral buttresses might render their necks effective clubs or wrestling appendages, particularly well suited to rapid, powerful downward motions. Summarised a little more succinctly: there is reason to think Brontosaurus and kin might've smashed the crap out of each other, or other animals...

...with their necks.

Yowsers. But outlandish as the Brontosmash hypothesis seems, it really isn't just idle speculation: a paper is in the works, the Taylor et al. SVPCA talk abstract is a preprint at PeerJ, and you can see the case explained in Mike's talk slides here. I find it pretty convincing myself: I mean, there had to be some reason apatosaurines had those crazy necks. Evolution is a sloppy craftsman at times, but the energy put into growing and maintaining such massive neck anatomy must've been substantial, and that almost certainly reflects a certain adaptive purpose. Combat might well have been that driving force. We also know from living animals - camels, giraffes and some seals - that necks are used for fighting, and that neck-based combat can promote reinforcement and restructuring of neck anatomy. It certainly sounds provisionally convincing to me, and I'm sure we'll hear a lot more about it in the future as the hypothesis is developed.

There're two nods to classic palaeoartists here. There's a Knightian influence to the style (not the first time he's infected my work), as well as, via the very upright postures of the wrestling animals, a hat-tip to Robert Bakker's famous 'boxing Brontosaurus' image. The latter had a big impact on me when I first saw it as a teenager, and it's been on my mind for obvious reasons with all this talk of fighting apatosaurines. I thought it also made for a bit of a contrast to Brian's 'official' depictions as well, these showing the animals in quadrupedal or near-quadrupedal poses (I assume at least some of the postures in those artworks mimic neck combat in elephant seals, a favoured modern behavioural analogue of Team Brontosmash). The setting is meant to be in the wetter, northern parts of the Morrison Formation palaeoenvironment, alongside swollen river margins. Initial plans were to record the progression of the wrestling match in muddy footprints, but adding splashes and visual noise to proceedings was too much fun, especially with those tails whirling around everywhere. Sloshing water provided a means showing specific actions, too, the splashes from colliding brontosaur hide signifying each powerful, multi-tonne impact. This was definitely a fun image to put together, and it's certainly a favourite of my recent work. Brontosmash!

That's all for now. Coming soon (probably): The Triassic! And a boring old pterosaur that we just can't leave alone!

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Who is this 'Mark Witton' chap?

Dr Mark Witton is a palaeontologist and palaeoartist, affiliated with the University of Portsmouth, UK. My technical research is focused on pterosaurs - Mesozoic flying reptiles - but my artwork has introduced me to a wide array of different fossil animals that are just as interesting. I work as a freelance author, consultant and artist: check out my work at MarkWitton.com, follow me on Twitter @MarkWitton, and browse my books here. Contact me at wittonprints[at]gmail.com. Due to volume of email I can't always reply to messages, but I do my best.